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Urethane: structure, properties, obtaining, uses

Ethyl carbamate is also used as a pesticide and fungicide. Until 1943 it had been used as an antineoplastic. But when its carcinogenic action was discovered in experimental animals, this application was discarded.

Sphere and rod representation of the ethyl carbamate or urethane molecule. Source: Kemikungen / Public domain

Urethane is produced industrially by the hot reaction of urea with ethanol. It is a volatile and flammable compound that has a vapor density three times that of air. Additionally, urethane undergoes sublimation.

Polyurethane, on the other hand, is a polymer whose industrial production is aimed at obtaining foams, used in furniture and as insulators in refrigerators. Despite its name, polyurethane is not a polymer of urethane itself, but is made up of different organic units.

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Urethane structure

In the first image we have the molecular structure of urethane. On the left side we have the carbamate group: R 2 NCOO-, with its alkyl groups R substituted by H, and the COO- segment linked to the ethyl substituent. As can be seen, it is a simple molecule, which alone does not offer many polymerization options.

Urethane properties

Names

-Urethane

-Ethyl carbamate (IUPAC name)

-Ethyl ester of carbamic acid

-Ethylurethane

Chemical formula

3 H 7 NO 2 or NH 2 COOC 2 H 5

Molar mass

89.094 g / mol

Physical appearance

White or colorless crystals. White powder of a granular nature.

Flavor

Refreshing salty taste

Odor

Lavatory

Density

1,056 g / cm 3

Melting point

46 to 50 ºC

Boiling point

182 to 185 ºC

Water solubility

4.8 · 10 5 mg / L at 15º C. It is very soluble, since it is a fairly polar molecular.

Solubility in other solvents

1 gram of urethane is dissolved separately in: 0.8 mL of alcohol, 1.5 mL of ether, 0.9 mL of chloroform, 2.5 mL of glycerol, and 32 mL of olive oil.

Vapor density

3.07 in relation to air as a unit.

Vapor pressure

3 Pa at 20 ° C.

Octanol / water partition coefficient

Log P = – 0.15

ignition point

92 ºC

Refractive index

1.4144 at 51 ºC

Sublimation

It sublimates rapidly at a temperature of 103 ºC and a pressure of 54 mm Hg.

Reactivity profile

Urethane is incompatible with alkalis, acids, coral hydrates, camphor, menthol, and thymol. It is also incompatible with antipyrine and salol. Reacts with Phosphorus Pentachloride to produce an explosive.

Obtaining

Synthesis

Urethane is produced by the hot reaction of urea with ethyl alcohol:

Equation for the reaction between ethanol and urea. Source: No machine-readable author provided. Oldsci assumed (based on copyright claims). / Public domain

Urethane is also produced by the reaction of ethyl chloroformate with ammonia.

Presence in fermented foods and beverages

The urethane present in some fermented beverages comes from the reaction of urea, caused by the metabolism of the amino acid arginine and released by yeast, with ethyl alcohol. So, urethane is a side product of yeast fermentation of glucose present in fruits.

Producers of alcoholic beverages make a determination of the presence of urethane, proceeding to discard batches of beverages that present levels higher than permitted, since urethane is a carcinogenic agent.

Toxicity

Besides being demonstrated the carcinogenic action of urethane in experimental animals, it has been possible to show numerous toxic effects on human beings. It is harmful by inhalation, skin absorption or by ingestion.

Urethane causes a burning throat, watery or bloody diarrhea, abdominal pain, decreased urine formation and excretion, arterial hypotension, cardiovascular collapse, delirium, seizures, muscle weakness with respiratory failure, and finally depression of the nervous system and of the bone marrow.

Applications

Medicine

Previously, urethane was used in the treatment of some types of cancers, especially chronic leukemia and multiple myeloma. In 1943, evidence was obtained that urethane had, on the contrary, a carcinogenic action, so this use was discarded.

It was also used as an analgesic, an application that was also abandoned. However, its use to relieve postoperative pain was continued in Japan until 1975.

Urethane is currently used as an anesthetic in animals used in experimental activities, finding in some cases an anesthetic action that lasts for more than 24 hours.

Urethane was part, along with sulfonamide, of a sclerosing solution used in the treatment of varicose veins.

Polyurethanes

One of the uses of polyurethanes is to serve as a material for skateboard wheels. Source: Aqazi1411 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Polyurethanes are polymers having diol and diisocyanate as usual monomers. That is, polyurethane is not a polymer of urethane (ethyl carbamate), but of another chemical compound referred to as urethane: carbamate (H 2 NCOO  ), which serves as a link between the chemical units that make up polyurethane.

They are used as foam in the manufacture of pressure-adaptive seats, in insulation panels of refrigeration equipment in the form of rigid foam, as seals and gaskets of microcellular foam.

They are also used in the manufacture of wheels and tires of great hardness, used in escalators, shopping carts in supermarkets, skateboard wheels. In addition, polyurethanes are used in the manufacture of suspension bushings for automobiles.

They are used in composites to coat electrical materials, in coatings and surface sealants, as a base for laying carpets, and as hard plastic parts. They are also used in the manufacture of clothing items, such as the lining of bras.

Others

Urethane is used in the production of amino resins. These are used as adhesive substances in the manufacture of plywood and plywood, used in the construction of houses and in the manufacture of furniture.

Urethane is used as a solvent in organic synthesis reactions. It is also used as a fungicide and pesticide, as well as in the textile industry for the production of products that intervene in permanent pressing.

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